Quantum Correlations In The Three Spin Heisenberg Spin Chain

Quantum Discord (QD) is a kind of measure method of quantum correlation (QC) in a bipartite system. In general, this correlation is different from entanglement, because quantum discord may be nonzero even for certain separable states. Therefore this kind of quantum correlation has received more attention due to its significant role in quantum information protocols. On the basis of the model of three-spin Heisenberg spin chain, the quantum correlations of the XXZ spin chain with three-spin interaction and the XX spin chain with magnetic impurities are respectively studied in this thesis. The relation between the quantum discord and related parameters is discussed numerically.Firstly, the quantum correlation of three-spin XXZ chain with three-spin interactions is investigated. The influence of three-spin interaction on the quantum discord is discussed in case of the ferromagnetic and anti-ferromagnetic. Meanwhile, The effect of some parameters changing (such as anisotropic and temperature) on the quantum discord is studied in detail. The results show that the QD is enhanced in increase of the three-spin interaction, and the QD would re-growth as increasing temperature in the ferromagnetic case. Additionally, the properties of QD in ground state are also discussed in this thesis. It shows that quantum phase transition is found when there exists three-spin interaction. Secondly, the influence of the magnetic impurity on the quantum correlation of the spin chain is studied. The properties of the QD on the first and the second qubit as well as on the first and the third qubit are discussed respectively by considering the model that the magnetic field only effect on the third qubit in the three-spin XX chain system. It is found that the QD would be enhanced with increasing magnetic field when the impurity is not located on any one of two qubits studied in the paper. Furthermore, the QD will reach maximal value1for the system with a ground state; However, when the impurity is located on one of two qubits, the QD will only increase and reach a certain value less than1, then decrease and tend to0with increasing the magnetic field.